Transistors, such as metal oxide semiconductor field-effect transistors (MOSFETs), are the core building block of the vast majority of semiconductor devices. Some semiconductor devices, such as high performance processor devices, can include millions of transistors. For such devices, decreasing transistors size, and thus increasing transistor density, has traditionally been a high priority in the semiconductor manufacturing industry.
Epitaxial stressor regions are frequently used to increase the mobility of carriers in the channels of the MOS transistors, and thereby achieve a corresponding improvement in performance. However, as device geometries shrink (e.g., in 32 nm technologies and smaller technologies), non-uniformities and variations in the stressor regions at different locations across the wafer have a greater impact on transistor parameters, such as drive current, threshold voltage, and Miller capacitance. Non-uniformity across the wafer can potentially affect the yield, performance, and minimum operating voltage characteristics of the devices on the wafer.